The invention relates to a hydraulic system for a motor vehicle having a convertible top which can be folded back, with a convertible-top control system which can be operated by a hydraulic pump.
Hydraulic systems of this type are frequently used in modern motor vehicles described as convertibles and are known from practical experience. For safety reasons the convertible top can only be opened or closed when the motor vehicle is at a standstill or when traveling at a low speed, for example of less than 10 km/h. The other control devices which are arranged in the motor vehicle serve, for example, for the activation of adjustable spring struts, a transmission control system or an additional steering system for a rear axle. In known motor vehicles these hydraulic control devices are activated via their own hydraulic circuits and via hydraulic pumps or pressure accumulators additionally arranged in the motor vehicle.
The invention is based on the problem of providing a hydraulic system of the type mentioned at the beginning in such a manner that it is constructed as simply as possible and can be produced cost-effectively.
According to the invention, this problem is solved in that in a hydraulic line, which leads to the convertible-top control system, there is arranged a controllable hydraulic valve for the activation of a further hydraulic control device for operating a further functional unit of the motor vehicle.
In one refinement the convertible-top control system and the further hydraulic control device are switched on at the same time, there being a clear distinction between the power consumption of the convertible-top control system and the control device as an alternative to this, the further hydraulic control device can be activated only with the convertible-top control system switched off.
This enables the hydraulic system according to the invention to be used for the activation of the further hydraulic control devices when the convertible-top control system is not in use. Since the two devices have approximately the same power requirement, the hydraulic pump does not need to be adapted for the system according to the invention. Because of this, the hydraulic system according to the invention is of particularly simple construction and can be produced cost-effectively. Since, thanks to the invention, in each case either the convertible-top control system or one of the further hydraulic devices can be activated, pressure fluctuations do not arise in the hydraulic lines. Therefore, only a small pressure accumulator or none at all is needed as a buffer for operation of the further control devices. This results in a further reduction in the structural design of the system according to the invention.
The system according to the invention requires a particularly small structural design if a control electronics unit of the hydraulic pump is provided for the activation of the hydraulic valve. Furthermore, a designated pressure level can be produced for each of the hydraulic control devices by the simultaneous activation of the hydraulic pump and of the hydraulic valve.
According to another advantageous development of the invention, mutual interference of two further control devices can be avoided if the hydraulic pump is designed for the conveying of hydraulic oil in both directions, and a hydraulic valve is arranged in each of the hydraulic lines leading to the convertible-top control system.
According to another advantageous development of the invention, a multiplicity of hydraulic control devices can be operated in a simple manner with particularly low outlay if a plurality of branches to the hydraulic control devices are arranged in one of the hydraulic lines leading to the convertible-top control system. If certain hydraulic control devices are only to be activated separately, this can be achieved via further hydraulic valves which can be controlled by the control electronics unit.
In the case of hydraulic control devices which can be activated in parallel, a drop in pressure in one of the hydraulic control devices when a further hydraulic device is switched on can be avoided in a simple manner if a nonreturn valve is in each case arranged between the branches and the control devices. Because of the nonreturn valves, discharging of the hydraulic oil from the hydraulic control device activated first is reliably avoided.
According to another advantageous development of the invention, a plurality of hydraulic control devices, which require the same volume flow of hydraulic oil at essentially the same time, can be operated with a small number of hydraulic lines if one hydraulic line is designed as a return line of one of the hydraulic control devices and as a supply line of a further hydraulic control device.
According to another advantageous development of the invention, a multiplicity of hydraulic control devices can be operated without mutual interference if a plurality of hydraulic valves, which in each case activate hydraulic control devices, are arranged in series in one of the hydraulic lines, each of the hydraulic valves being formed as a shuttle valve. By means of this design, when one hydraulic control device arranged close to the hydraulic pump is activated, all of the hydraulic control devices arranged further away are automatically switched off. Each of the hydraulic control devices is hereby assigned a priority. The convertible-top control system can therefore be arranged next to the hydraulic pump and, for example, the hydraulic control device for the rear-wheel steering system can be arranged in second place.